1. Field of the Invention
The present invention relates to a method of providing voice suggested distance by a navigation software, and more particularly, to a method of dynamically adjusting a voice suggested distance for a global positioning system (GPS) navigation software based on a current driving speed.
2. Description of the Related Art
In 1973, the US Department of Defense started developing a precise satellite navigation and positioning project, called Global positioning system (GPS), which would cost over 12 billion US dollars. The project took more than 20 years. The first GPS satellite was launched in 1978, and 3D, all-weather positioning operation has been formally introduced since October 1993. Originally, the development of the GPS is only for supporting the military aviation and airplane requirements. Now, the GPS is opened to public usage, which inevitably brings a revolutionary change to our daily life. For example, for moving automobiles or ships, it is possible to obtain an accurate arrival time and an optimal trip route to the destination. The ambulance can perform the emergency mission with more efficiency. In addition, with the help of the electronic map, the car drivers can get a picture about the current location and the trip route to the destination. With accurate 3D positioning function, the GPS can be applied in the airplane navigation system in the airport control tower to prevent collisions, as well as the extremely precise zero-visibility landing system. In 1992, more than 130 GPS work items had been clearly defined by US Department of Forest Service based on its characteristics and its possible applications (Greer, 1993).
In general, a GPS configuration is composed of a space segment, a control segment, and a user segment.
The space segment represents the GPS satellites operating in the space. Although there are only 26 GPS satellites operating in the space now, only 24 satellites are actually required for receiving signals from 4˜8 satellites anytime and anywhere simultaneously to perform the 3D positioning function, and the other two are spare satellites. The orbit period of all GPS satellites is 12 hours, which indicates the satellite circles the earth two rounds a day. Every GPS satellite has been installed 4 extremely precise atomic clocks for spare use, two of which are the Rubidium (Rb) atomic clocks, and the other two of which are the Cesium (Cs) atomic clocks. If the precision is measured by an error of one second, the precision of the Ru atomic clock is about 30K years, and the precision of the Cs atomic clock is about 300K years (Leick, 1990). The basic frequency of the atomic clock is 10.23 MHz, the multiples of which are used to form a C/A code (with a frequency of 1.023 MHz) and a PRN (Pseudo Random Noise) of a P code (with a frequency of 10.233 MHz). The codes mentioned above are modulated on a L1 carrier (with a frequency of 154*10.23 MHz and a wavelength of 19 cm) and a L2 carrier (with a frequency of 120*10.23 MHz and a wavelength of 24 cm), then the codes are finally modulated to a 50 BPS (bits per-second) dual-frequency radio signal broadcasting to the earth continuously. The reasons for modulating these codes on the carriers are: A. for obtaining a distance between the satellite and the receiver by measuring a time difference between the codes; B. for recognizing various types of satellites; C. for restraining the unauthorized use; and D. for eliminating impacts due to the non-geometrical factors.
The control segment of the GPS has been completed in September 1985. The control segment comprises a main control site, three ground antennas, and five monitor sites. Each monitor site comprises a dual-frequency GPS reception site, a standard atomic clock, a sensor, and a data processor. In addition, a WGS 84 coordination is provided through precise measurement by the US Department of Defense Cartography Service. Each monitor site is configured to continuously track each of the satellites 24 hours a day. In addition, an observed virtual distance obtained every 1.5 second, the observed weather data, and an ionization layer data are calculated together, so as to obtain a set of smoothed data every 15 minutes. Then, the smoothed data is transferred to the main control site. Located in the united space control center in Springfield, Colo., the main control site mainly receives various data transmitted from those five monitor sites, to calculate the satellite calendar data, the modification parameter of the satellite clock, and the modification parameters of the ionization layer delay for the ground antennas and then to the satellite in order to update the data in the satellite. The main control site is configured to calculate the modification of the satellite orbit, while sending the control signal, or replacing the malfunction satellite with the spare satellite. The ground antenna transmits the data to the satellite via an S-channel radio wave. A set of data is continuously sent back to the satellite every 8 hours under normal operation. The whole mission of the control segment is to keep the satellite operating in a precise orbit, to feed the update information back to the satellite, and to monitor each satellite for ensuring normal operation.
The user segment refers to a receiver which is used to receive the GPS satellite signal. Since the GPS is widely used in different applications, users may choose a receiver based on the required function and precision. For example, when it is applied to an application of measurement, at least a receiver, a recorder, a monitor, an embedded antenna or an external antenna, a data processor, such as Personal Digital Assistant (PDA) or a Personal Computer (PC), and a power supply are required.
Since more and more car manufacturers have made GPS a standard equipment, in the near future, drivers can better locate their position in a unfamiliar place without having to steer the wheel at one hand, and hold a map in the other hand trying to figure out the route to the destination. The GPS available in the market now provides a preset distance, before reaching a turn or a destination, regardless of the driving speed. That is, before coming to a turn or a destination, the system notifies the driver the left distance (suggested distance) before making a turn with a voice alarm. However, when driving at a high speed, the driver may miss the turn or destination because the suggested distance is too short, which is time wasting. Or when driving at the wrong lane, the driver needs to change the lanes suddenly, which may result in accidents in split second.